1. Field of the invention
This invention relates to a laser deposition method and apparatus in which laser light is irradiated to a target to generate a laser induced plasma such that only a part of the material, emitted from the target in a predetermined direction, is selectively deposited on a substrate.
2. Description of the Related Art
Heretofore, a variety of films and particularly thin films have been used as anti-reflection films for optical parts, such as camera lens, and also in surface coatings for ornaments. As great advances have recently been made in electronics, the irradiation deposition for thin films to the wiring of semiconductor devices, ICs, LSIs, etc. as well as to magnetic recording materials has been on the rise.
Further, upon progress of study on thin films, it has turned out that various peculiar effects such as tunneling effect could be achieved with thin films and also that shaping the material into a thin film could cause the structure of the material to change, depending on which various new functions and features could be provided. Accordingly, the significance of films is increasing throughout various fields.
Known film manufacturing technologies are exemplified by a vacuum deposition method in which particles of a film material are caused to evaporate in high vacuum and the evaporated particles are deposited over a substrate, and a sputtering method in which ions are irradiated to a target (an object) to cause atoms and molecules of the target surface to evaporate and then to be deposited over a substrate. Other film manufacturing technologies may be adopted depending on the kind of a film to be produced.
By utilizing plasma and ions in the conventional film production, the following effects can be obtained:
(1) It is possible to clean the substrate surface on which a film is to be formed, causing an improved degree of close adhesiveness. PA1 (2) It is possible to control the property, such as crystallinity, of a film to be formed. PA1 (a) Ion plating method, in which evaporated particles are ionized in plasma, and accelerated by an electromagnetic field for deposition on the substrate. PA1 (b) Cluster ion beam method, in which a cluster of about 1,000 atoms or molecules is formed by adiabatic expansion and ionized, then accelerated and deposited over the substrate. PA1 (c) Ion beam method, in which ions formed in an ionization unit are irradiated to the target. PA1 (d) Ion beam enhanced deposition method, in which particles are evaporated by an ion beam and ionized, then deposited on the substrate.
Following are methods for positively utilizing the above effects of plasma and ions:
However, the above methods have several problems on preparations of thin films.
In the ion plating method (a) and the ion beam method (c), particles are evaporated and ionized by gaseous plasma and discharge of an inert gas such as argon. Therefore, these methods cannot be used in high vacuum so that impurities contained in the film can be minimized only inadequately. This is partly because inert gas contains impurities, which can be mixed in the film and partly because inert gas itself can be mixed in the film as impurities.
Further, in the ion plating method (a), the cluster ion beam method (b) and the ion beam enhanced deposition method (d), an evaporation source and ionization unit for evaporating a material are provided independently of each other, thus making the entire apparatus bulky and complex.
In addition, in any of the methods (a) through (d), since most of the ions of the film material to be evaporated are singly charged, it is impossible to produce a film of a peculiar characteristic in which multiply charged ions are selectively utilized. Also, there have been, heretofore, many restrictions to the selection of the material to be evaporated so that a film having a desired quality could not be formed.
Furthermore, in the case of a multilayer film composed of a plurality of superimposed films or a mixed film formed of a mixture of a plurality of materials, evaporation sources are needed one for each material to be evaporated, which makes the entire apparatus very bulky.
Another known method is a laser deposition method in which laser light is focused and irradiated to a target to evaporate an emitting material from the target so that evaporated particles are deposited on the substrate. This prior art method is exemplified by Japanese Patent Laid-Open Publications Nos. 116373/1984 and 43929/1989. In these prior laser deposition methods, since there is provided no means for selecting the emitting material emitted only in a predetermined direction, a film having an undesired characteristic would also be formed.